Locomotive

A
locomotive is a railwayvehicle that provides the motive
power for a train,
and has no payload capacity of its own; its sole purpose is to move the train
along the tracks. Many trains feature self-propelled payload-carrying vehicles;
these are not normally considered locomotives, and may be referred to as multiple
units or railcars; the use of these self-propelled
vehicles is increasingly common for passenger trains, but
very rare for freight (see GermanCargoSprinter).
Vehicles which provide the motive power to haul an unpowered train, but are not
generally considered locomotives because they have payload space or are rarely
detached from their trains, are known as power
cars.

Traditionally,
locomotives haul their trains. Increasingly common these days in passenger service
is push-pull operation, where the
locomotives push the trains in one direction, and are controlled from a control
cab at the opposite end of the train in the other.

Hagley
Hall steam locmotive on display in the restaurant area of the McArthur Glen Shopping
Centre, Swindon, England

Benefits
of locomotives

There
are many reasons why the motive power for trains has been traditionally isolated
in a locomotive, rather than in self-propelled vehicles. These include:

Ease of maintenance
- it is easier to maintain one locomotive than many self-propelled cars.

Safety
- it is often safer to locate the train's power systems away from passengers.
This was particularly the case for the steam locomotive, but still has
some relevance.

Easy
replacement of motive power - should the locomotive break down, it is easy
to replace it with a new one. Failure of the motive power unit does not require
taking the whole train out of service.

Efficiency
- idle trains do not waste expensive motive power resources. Separate locomotives
mean that the costly motive power assets can be moved around as needed.

Obsolescence
cycles - separating the motive power from the payload-hauling cars means that
either can be replaced without affecting the other. At some times, locomotives
have become obsolete when their cars are not, or vice versa.

Classification
by motive power

Locomotives
may generate mechanical work from fuel,
or they may take power from an outside
source. It is common to classify locomotives by their means of providing motive
work - the common ones include:

Steam

The
first railway locomotives (19th century) were powered
by steam, first by burning wood, later coal or oil. Because of the steam engine,
some people took to calling the steam locomotives themselves "steam engines".
The steam locomotive remained by far the most common type of locomotive until
after World War II. The age of
steam correlates highly to the coal
era.

The
all-time speed record for steam trains is held by an LNER Class
A44-6-2Pacific locomotive of the LNER in England, number
4468 Mallard, which pulling
six carrriages (plus a dynamometer car) reached 126 mph (203 km/h) on a slight
downhill gradient down Stoke Bank on 3 July1938. Aerodynamic passenger locomotives
from other countries such as Germany and the United States attained speeds very
close to this, and this is generally believed to be close to the practicable upper
limit for the direct-coupled steam locomotive.

Before
the middle of the 20th century, electric and
diesel-electric locomotives began replacing steam locomotives. Steam locomotives
are less efficient than their more modern diesel and electric counterparts and
require much greater manpower to operate and service. British
Rail figures showed the cost of crewing and fuelling a steam locomotive was
some two and a half times that of diesel power, and the daily mileage achievable
was far lower. As labour costs rose, particularly after the second world war,
non-steam technologies became much more cost-efficient. By the end of the 1960s-1970s,
most western countries had completely replaced steam locomotives in commercial
service. Freight locomotives generally were replaced later. Other designs, such
as locomotives powered by gas turbines, have been experimented with, but seen
little use.

By
the end of the 20th century, almost the
only steam power still in regular use in North America and Western
European countries
was on railroads specifically aimed at tourists and/or railroad enthusiasts, known
as railfans or train
spotters, although some narrow gauge lines in Germany
which form part of the public transport system, running to all-year-round timetables
retain steam for all or part of their motive power. Steam locomotives remained
in commercial use in parts of Mexico into the late 1970s. Steam locomotives
are in regular use in China, where coal is a much more abundant resource
than petroleum for diesel fuel. India
has switched in the last decade from steam-powered trains to electric- and diesel-powered
trains. In some mountainous and high altitude rail lines, steam engines remain
in use because they are less affected by reduced air pressure than diesel engines.

See
also

Diesel-mechanical

Diesel
locomotives vary in the form of transmission used to convey the power from
a diesel engine (or engines)
to the wheels. The most simple form of transmission is by means of a gearbox, in the
same way as on road vehicles. Diesel trains or locomotives that use this are called
diesel-mechanical and began to appear (although limited in power) even before
the first world war which
saw a number of simplex diesel systems built for the war, a small number of which
survive and are still operational today.

It
has, however, been found impractical to build a gearbox which can cope with a
power output of more than 400 horsepower (300 kW) without
breaking, despite a number of attempts to do so. Therefore this type of transmission
is only suitable for low-powered shunting locomotives, or lightweight
multiple units or railcars.

For
more powerful locomotives other types of transmission have to be used.

Diesel-electric

The
most common form of transmission is electric; a locomotive using electric transmission
is known as a diesel-electric locomotive. With
this system, the diesel engine drives a generator or alternator;
the electrical power produced then drives the wheels using electric motors. In effect,
such a locomotive is an electric locomotive which carries its own generating station
along with it.

Early
diesel-electrics were switching engines used to move rail cars around in rail
yards. The first went into service in 1924. A decade later, the technology
first began to be applied to regular rail service as streamliners went into service.
Actually, a gasoline-electric system powered
the first such train, but diesel-electric systems soon proved to be more cost-effective
because of higher efficiency and lower maintenance costs. The fuel for one early
high-speed run from Chicago, Illinois to Denver, Colorado only
cost US$14.64 (in 1934 dollars).

In
the 1970s, British
Rail in the United Kingdom developed a high-speed diesel-electric train called
the High Speed Train or HST.
This train consists of two Class 43 locomotives
(also known as power cars), one at each end, and a number of "Mark 3" carriages
(usually 8). A complete HST set was originally designated as a Class 253 or 254
diesel multiple unit
(DMU), but due to the frequent exchanges between sets the power cars were reclassified
as locomotives and given class number 43. The unpowered carriages were simultaneously
reclassifed as individual coaches - the number of a DMU set should identify all
its associated carriages as well.

The
prototype HST (designated Class 252) holds the world speed record for diesel traction,
having reached a speed of 143 mph, although the operating speed of the production
HST in service is 125 mph (200 km/h), hence the name "Inter-City 125".

A
variant of the Intercity 125, the XPT, is in service on New
South Wales railways in Australia, but with a lower
top speed and different carriages.

Diesel-hydraulic

Alternatively,
diesel-hydraulic locomotives use hydraulic transmission to convey
the power from the diesel engine to the wheels. On this type of locomotive, the
power is transmitted to the wheels by means of a device called a torque converter. A torque
converter consists of three main parts, two of which rotate, and one which is
fixed. All three main parts are sealed in a housing filled with oil. Many diesel-hydraulic
multiple units also have a "fluid flywheel" which acts as a "second gear" for
running at higher speeds.

The
inner rotating part of a torque converter is called a centrifugal pump
(or impeller), the outer part is called a turbine wheel (or driven wheel),
and between them is a fixed guide wheel. All of these parts have specially shaped
blades to control the flow of oil.

The
centrifugal pump is connected directly to the diesel engine, and the turbine wheel
is connected to an axle, which drives the wheels.

As
the diesel engine rotates the centrifugal pump, oil is forced outwards at high
pressure. The oil is forced through the blades of the fixed guide wheel and then
through the blades of the turbine wheel, which causes it to rotate and thus turn
the axle and the wheels. The oil is then pumped around the circuit again and again.

Diesel-hydraulic
locomotives are slightly more efficient than diesel-electrics, but were found
in many countries to be mechanically more complicated and more likely to break
down. In Germany, however, diesel-hydraulic systems achieved extremely high reliabily
in operation. Persistent argument continues over the relative reliability of hydraulic
engines, with continuing questions over whether data was manipulated politically
to favour local suppliers over German ones. In the US and Canada, they are now
greatly outnumbered by diesel-electric locomotives, while they remain dominant
in some European countries. The only diesel-electric locomotives of the Deutsche
Bundesbahn were BR 288
(V 188), of which 12 were built in 1939 by the DRG.

Gas
turbine

Locomotives
powered by gas turbines were developed
in many countries in the decades after World War II. These used
jet-type engines (similar to the turboshaft engines in a turbine
helicopter) driving an output shaft. The normal method of transmitting power to
the wheels involved an electrical transmission similar to a diesel-electric locomotive
- the turbines running at constant speed driving a generator, feeding to large
electric motors driving the wheels.

Gas
turbine locomotives are very powerful, but also very noisy (they sounded rather
like a jet aircraft). Union Pacific operated the
largest fleet of turbine locomotives and used them extensively, at one point claiming
that the turbines hauled 10% of the railroad's freight. Their efficiency was quite
low, but this was initially not a problem; fuel was cheap, and Union Pacific's
gas turbines were fuelled with cheap 'Bunker C' heavy oil. This cheap fuel source
vanished when improved refinery techniques allowed it to be 'cracked' into lighter
petroleum grades. After the oil crisis in the 1970s and the rise in
fuel costs, gas turbine locomotives became uneconomic to run, and many were taken
out of service. This type of locomotive is now rare. None are in use in the United
States.

Electric

Virginian Railway in
West Virginia and Virginia electrified a 134-mile stretch through rugged mountainous
territory. Electric locomotive 100 was built by ALCO-Westinghouse in 1926.
Photo courtesy of Virginian Railway Enthusiasts Group on Yahoo

The
electric locomotive
is supplied externally with electric power, either through an overhead pickup or through
a third-rail. While the cost
of electrifying track is rather high, electric trains and locomotives are significantly
cheaper to run than diesel ones, and are capable of superior acceleration as well as regenerative braking,
making them ideal for passenger service in densely populated areas. Almost all
high speed train systems
(e.g. ICE, TGV, bullet train) use electric
power, because the power needed for such performance is not easily carried on
board. For example the most powerful electric locomotives that are used today
on the channel tunnel freight
services use 7MWatts of power.

The
world speed record for a wheeled train was set in 1990 by a French TGV which reached
a speed of 515.3 km/h (320 mph).

A
small number of electric locomotives can also operate off battery power to
enable short journeys or shutning to occur on non-electrified lines or yards.
Pure battery locomotives also found usage in mines and other underground workings
where diesel fumes or smoke are not safe and where external electricity supplies
could not be used. Battery locomotives are also used on many underground railways
for maintenance operations as they are required to operate in areas where the
electricity supply has been temporarily disconnected.

Electro-diesel

These
are special locomotives that can either operate as an electric locomotive
or a diesel locomotive. Dual-mode diesel-electric/third-rail locomotives are
operated by the Long Island Rail Road
and Metro-North Railroad
between non-electrified territory and New York City because of
a local law banning diesel-powered locomotives in Manhattan tunnels. For the same
reason Amtrak operates a fleet of dual-mode
locomotives in the New York area. British Rail operated dual
diesel-electric/electric locomotives designed to run primarily as electric locomotives.
This allowed railway yards to remain un-electrified as the third-rail
power system is extremely hazardous in a yard area.

Magnetic
levitation

The
newest technology in trains is magnetic levitation
(maglev). These electrically powered trains have a special open motor which floats
the train above the rail without the need for wheels. This greatly reduces friction.
Very few systems are in service and the cost is very high. The experimental Japanese magnetic levitation train
has reached 552 km/h.

The
first commercial maglev trains ran in the 1980s in Birmingham, United
Kingdom, providing a low-speed shuttle service between the airport and its
railway station. Despite the huge interest and excitement in the technology it
was abandoned and replaced by a cable-hauled guideway a few years later.

Classification
by use

The three
main categories of locomotives are often subdivided in their usage in rail transport operations.
There are passenger locomotives, freight locomotives and switcher (or shunter)
locomotives. These categories mainly depend on manoeuvrability, traction power
and speed. Some locomotives are designed to work in mountain railways.